Not Applicable.
1. Field of the Invention
This invention relates to a thin film cover constructed PVC and more specifically to a cover which is approximately 0.0025 inches in thickness throughout a major portion of its plan area, but which includes an open mouth portion defined by a considerably thickened rim or bead and an adjacent marginal portion which tapers in thickness from the bead toward the main body of the cover. Also disclosed is a preferred method for forming the cover.
2. Description of Related Art
The following prior U.S. Patents disclose articles which are coated through the use of methods which are somewhat similar to the method disclosed in the instant invention:
However, the coated articles disclosed by the above-noted patents, the articles formed in part by coating and the methods involved in the above-noted prior patents are not equivalent to the article of the instant invention or the method utilized in forming the article.
The article of the instant invention is similar to the apparatus or lid disclosed in U.S. Pat. No. 4,901,881 in that it is designed for use as a closure. However, U.S. Pat. No. 4,901,881 discloses a closure formed of a latex elastomeric material and which must be formed utilizing a method which is considerably different from the method by which the closure of the instant invention is formed.
The cover of the instant invention is formed of polyvinyl chloride compounded to provide a material which is highly flexible, relatively non-flammable, hard-wearing and resistant to water and corrosion. Polyvinyl chloride is an ethanoid polymer produced as a fine white powder by both emulsion polymerization and suspension polymerization of the gas, vinyl chloride, when liquified under nitrogen pressure. The terms xe2x80x9cPVCxe2x80x9d and xe2x80x9cvinylxe2x80x9d are commonly used with reference not only to the polymer, but to all materials of which polyvinyl chloride is a constituent. PVC composition are prepared by hot mixing the polymer with plasticizers and small proportions of stabilizers, stearate lubricants, and coloring materials to give materials of a wide range of hardness, from rigid (with little or no plastizer) to very soft (equal proportions of plastisizers and polymer), and in a wide range of colors, as well as crystal clear.
The polyvinyl chloride utilized in producing the cover or article of the instant invention is termed as a plastisol thermosetting plastic. Once compounded, plastisols need heat to transform them into a solid. They usually are placed in molds and as the heat increases, the plastisol passes from a liquid, through a gel phase and finally becomes a solid. Heat is then continued to cure the solid mass and give it its final properties.
The latex elastomeric material utilized in producing the cover disclosed in U.S. Pat. No. 4,901,881 may have minute particles of latex rubbed therefrom by friction and there are many potential environmental uses for a flexible cover and the like for which a latex elastomeric material is not desirable because of the possibility of contamination by minute particles of latex rubber when covers of this material are used.
Plastisols, on the other hand, when properly compounded and cured, are reasonably elastic, highly tear-resistant, pliable, and relatively soft to the touch without being excessively resilient. It is also pointed out that the polyvinyl chloride cover of the instant invention may be formed in generally one-half the time required to form a similar cover constructed of a latex elastomeric material, in that the latex elastomeric material requires a considerably longer curing time.
The main object of this invention is to provide a flexible cover which will have many uses.
Another object of this invention, is to provide a flexible cover which will be at least somewhat elastomeric, thereby enabling a cover, such as that produced for covering an open top container, to be manufactured in different sizes but capable of being usable to cover not only specific sizes of containers but also containers of at least slightly varying sizes.
Another important object of this invention, to provide a cover of the thin film type which may be reliably produced, without xe2x80x9cpinholesxe2x80x9d.
Still another object of this invention is to provide a flexible thin film cover incorporating not only a molded thickened peripheral bead (as opposed to a rolled bead) but also an outer marginal portion immediately adjacent the thickened bead which tapers gradually toward the main central body portion of the cover, to thereby provide an outer peripheral portion of the cover which may be more securely sealed relative to an associated container.
Another object of this invention is to provide a flexible, film-type cover which may be readily molded against a concave mold surface.
Still another object of this invention is to provide a flexible, thin-film cover which may be individually produced over a considerably shorter time period than a similar cover constructed of latex rubber material.
Another object of this invention is to provide a method of manufacturing the cover of the instant invention which incorporates not only centrifugal force but also gravity in a manner such that the main body of the cover is of a substantially constant thickness, the open mouth of the cover is defined by a thickened reinforcement bead and a peripheral zone of the cover immediately adjacent the reinforcement bead gradually tapers in thickness from the bead toward the central body portion of the cover.
A final object of this invention to be specifically enumerated herein is to provide a cover which will conform to conventional forms of manufacture, be useable in numerous environments, be resistant to light abrading independent of minute particle deterioration and reliable throughout a wide range of usage.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.